When observing a threaded fastener, such as a bolt, machine screw or the like, an observer cannot determine, by sight alone, the torque that has been applied to the threaded fastener. For example, an observed head of a bolt, that has only been hand tightened into a tapped hole, has the same appearance as a bolt that has been mechanically driven into the tapped hole at a high torque. During the manufacturing and assembly procedures of many devices, it is often the responsibility of an assembler to tighten certain threaded fasteners to a predetermined torque. However, due to human error, equipment failure or the like, it is not uncommon for an assembler, or even an automated machine, to fail to tighten all the threaded fasteners to their required torques. Additionally, since a loosely torqued threaded fastener has the same appearance as a properly torqued threaded fastener, it is very difficult to detect the undertorqued fastener during a quality control inspection. As such, undertorqued threaded fasteners may pass through the manufacturing procedure undetected, thereby compromising the engineered integrity of the device into which the undertorqued threaded fastener has been assembled.
In certain applications, the presence of a loose threaded fastener may result in the eventual failure of the entire device into which the threaded fastener was assembled. Additionally, in certain applications such as aircraft, spacecraft, high speed industrial machinery and the like, the failure mode caused by the loose threaded fastener may represent a danger to the lives of people. As such, in many fields of manufacture, the torque of certain critically positioned threaded fasteners must be checked in a separate operation, to assure for a proper assembly. The extra procedural step of testing the torque of threaded fasteners therein adds to both the cost and complexity of the manufacturing process.
In many other applications, the improper torque applied to a mechanical fastener does not represent a risk to the life of people or a risk to the overall performance of the device. However, an undertorqued threaded fastener may result in a loose part, the failure of a non-essential subcomponent or cause an undesired "rattle" in the assembly. Such defects in manufactured goods result in returned goods, warranty repairs and dissatisfied customers. The quality of manufactured goods is becoming increasingly more important to consumers in today's competitive markets. As such, manufacturers are now incurring increased manufacturing costs to ensure that even non-essential threaded fasteners are assembled at the proper torque, so as to assure quality and prevent customer dissatisfaction.
The present invention torque indicator is a device shaped in the general form of a split-ring washer that is placed around the shaft of the threaded fastener, below its head. The present invention is shaped so as to expand when the threaded fastener is tightened, breaking free of the threaded fastener at a predetermined torque. In the prior art there exist many different split-ring washers that are made to be used with threaded fasteners. Many prior art split-ring washers even have a shaped cross-sectional geometry that are designed to interact with the head of a threaded fastener. Such prior art split-ring washers are exemplified by U.S. Pat. Nos. 467,107 to Wiley, 646,226 to Kleman, 1,849,406 to McCrudden and U.S. Pat. Nos. 1,876,834, 1,876,835 and 1,876,836 to Berge. However, in the art of split-ring washers, the expansion of the split ring washer, as the threaded fastener is tightened, is a highly undersirable characteristic. Consequently, the prior art split-ring washers are shaped to match the contour of the head of the threaded fastener or a set into shaped reliefs to deter the expansion of the washers when a torque is applied to threaded fasteners.
The present invention, although having the general appearance of a split-ring washer, is formed to have a function entirely different from that of a typical prior art split-ring washer. The objective of the present invention is to set forth a device that can be used in conjunction with a threaded fastener so as to give a positive, easily viewed indication as to whether a certain threaded fastener has been tightened to a proper torque value.